This invention relates to electrical devices in general, and, more particularly, to electrical devices for use with electric storage batteries that have a bi-level battery state-of-charge indicator incorporated in the device.
Electric storage battery packs are widely used in the electro-motive industry to provide electrical power for electrically driven vehicles such as, fork-lift trucks. The battery pack is connected to the vehicle's drive system through a plural conductor battery cable and electrical connector. Representative examples of such electrical connectors are shown in U.S. Pat. Nos. 3,091,746 and 3,794,957.
Typically, in multi-vehicle applications, the discharged battery pack, together with its attached battery cables and electrical connector, is removed from the vehicle after a duty cycle. The discharged battery pack is replaced with a freshly charged battery pack from the "battery room". The removed discharged battery pack is then recharged along with other discharged battery packs in the "battery room".
It is desirable that the "battery room" operator know the charge states of the various battery packs in the "battery room" so that only fully charged battery packs are placed in the vehicles. Various methods are currently employed to determine the charge states of the batteries. The specific gravity of the electrolyte in each battery cell can be measured with a hydrometer to provide an indication of the charge state of the individual cell and, cumulatively, of the battery itself. However, this method is both tedious and time consuming for the "battery room" operator.
Many modern battery chargers contain an indicator, such as a lamp, to show the charge state of the battery under charge on the charges. In such chargers when the battery reaches a preselected state-of-charge, the indicator provides a suitable indication, e.g., the indicator lamp goes on. Generally, the achievement of the preselected state-of-charge is determined by monitoring the battery voltage. When the battery voltage reaches a preselected percentage of the fully charged battery voltage, the indicator lamp is turned on and will remain on until the battery is disconnected from the charger.
In the battery-motive industry the battery voltage for indicator lamp "turn on" is generally referred to as the "TVR" voltage after the "timer-voltage-relay" and, typically, equals approximately 90% of the fully charged battery voltage. Although the battery charger indicator provides an indication of the charge state of the battery or batteries in a battery pack, it is operative and useful only as long as the battery or battery pack is connected to the charger.
In a busy "battery room" operation, the battery charger(s) is used to charge a number of battery packs during a shift. The freshly charged battery packs are stored for later replacement in vehicles. Once the charged battery packs have been removed from the charger, the "battery room" operator no longer has an indication of the charge condition of the battery pack. It is not at all unusual for a "battery room" operator to become confused as to the charge state of a particular battery pack and to replace a discharged battery pack with another discharged battery pack. The discharged replacement battery pack may still have a sufficient charge to allow the vehicle operator to drive the vehicle for some short period of time. Thereafter, when the battery pack fails, the vehicle must be towed back to the "battery room" or another battery pack must be delivered to the vehicle. Both operations are time consuming and costly.
It is accordingly an object of the invention to provide an electrical device for use with electric storage batteries that has a bi-level battery charge state indicator incorporated in the device.
It is another object of the invention to provide such an electrical device in which the battery charge state indicator produces an indication when the battery reaches a pre-selected state-of-charge during charging and continues to produce such an indication until the battery has been discharged to a preselected state.
It is a feature of the invention that the bi-level battery charge state indicator of the electrical device continues to provide an indication of the battery's charge state after the battery has been disconnected from the battery charger.